1. Field of the Invention
This invention relates to methods for applying adhesive films to surfaces. More particularly, the present invention relates to methods for applying adhesive films to surfaces in such a manner that the resultant shape of the film closely matches the shape of the underlying surface.
2. Description of the Related Art
Adhesive films find many uses in modern commerce. For example, large graphic images used in advertising and other public displays are printed on films adhered to walls and other surfaces by means of pressure activated adhesives. As used herein, the term pressure activated adhesive will include conventional tacky pressure sensitive adhesives as well as adhesives (including repositionable adhesives) which may contain particulates, adhesive microspheres, microreplicated topographies, or other like adhesive systems in which adhesion is initiated by pressure applied between the adhesive and the substrate to be adhered.
Since many of the surfaces to which adhesive graphic films are to be adhered contain protrusions, depressions and other irregularities, it is useful to use films which are readily conformable to such surfaces, or to use thermoplastic films which can be made conformable by heating. It is common practice in the installation of such materials to first laminate the film to a surface using reasonable care to produce a smooth lamination, without wrinkles, followed by more localized lamination procedures such as pressing with pads or brushes and piercing areas of entrapped air. In the case of thermoplastic films, conformance can be further aided by selective heating of the film in areas of surface irregularity while applying pressure by means of resilient tools such as pads and brushes in order to conform the film to the surface. It is also common practice to pierce detached regions, for example bubbled areas, to allow release of trapped air while pressing down on the detached region to produce conformance and adhesion. A useful tool for producing holes for the release of air is disclosed in U.S. Pat. No. 6,311,399, wherein resiliently mounted pins press against a laminated film and penetrate the film in areas of air entrapment, so as to provide paths for the release of entrapped air. Entrapped air in detached regions may also escape through channels within the adhesive layer. Adhesive systems such as Comply™ Performance Graphic Marking Films, commercially available from 3M Company, and disclosed in U.S. Pat. No. 6,197,397, comprise microstructured channels within the adhesive layer that allow escape of entrapped air.
While various adhesive films, especially thermoplastic adhesive films, have found wide commercial application, there remains a need for easier and faster methods of conforming graphic films to irregular substrates such as riveted structures that are commonly found on semi-trailers and truck van bodies. Since riveted structures tend to have large numbers of rivet heads requiring treatment to improve conformance, the speed of performing this operation becomes especially important. There is also a need for a method of conforming films to irregular surfaces with less risk of damage to the surface of such films. Some protection against surface damage, either during lamination or during subsequent use, may be provided by laminating a transparent protective film, or overlaminate, over a graphic film. However, when such overlaminates are used, the overall film construction becomes thicker and therefore stiffer, which may make conforming of the film to surface irregularities more difficult.
The risk of damage to the film becomes greater when brushes or pads are used to press heat-softened thermoplastic films into conformance with irregular surfaces. Moreover, the current methods of conforming films to irregular surfaces are often physically demanding, in that they require not only skill, but also a significant amount of physical strength and endurance. Additionally, current methods can be ergonomically demanding, in that they often require simultaneous use of a heat source and several other tools, such as an air release tool for producing air release holes in the film along with a brush or pad for pressing the film into contact with the surface. The task is made more difficult by the environment in which this must be done, for example, by standing next to the side of a semi-trailer or other large surface.